The goal of this project is to define and understand the process by which colon cancer develops and spreads through the body. Two human colon carcinoma cells with almost identical genetic background were studied to determine what factors determine biologic behavior. The WiDr cell line is tumorigenic but non-metastatic in nude mice, while the HT-29 cell line is both tumorigenic and highly metastatic. Studies were done to establish whether this difference correlates with a) oncogene expression or mutation or b) susceptibility to apoptosis. A. Oncogene screening. Both cell lines showed an identical mutation in the p53 gene with no mutations in K-ras. Preliminary studies show that the WiDr cell line expresses higher levels of myc message than does the HT-29 cell line. B. Apoptosis. Cells in culture were treated with a topisomerase inhibitor, camptothecin. Using a newly developed flow cytometry assay for apoptosis, in which cells are incubated with fluorescein diacetate and preputium iodide, it was found that the HT-29 cell line was much more resistant to the induction of apoptosis than the WiDr cell line. These recent results are consistent with the notion that overexpression of myc may increase susceptibility of tumor cells to apoptosis, and that susceptibility to apoptosis, at least in this paired cell line model, may inhibit the ability of cells to metastasize.